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List:       xml-cocoon-users
Subject:    Re: Easy way to transformer parameters into a pipeline ??
From:       Christian Haul <haul () dvs1 ! informatik ! tu-darmstadt ! de>
Date:       2003-09-05 15:22:53
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On 05.Sep.2003 -- 04:54 PM, Lionel Crine wrote:
> 
>  wrote:
> >Passing parameters down the pipe out-of-band (IOW by not adding a tag
> >that travels down the pipe in-band like the rest of the data) is a
> >dangerous thing as you have no idea about the actual
> >schedule. Usually, a SAX event callback is completely propagated down
> >the pipe before the next callback is invoked. However, by using
> >buffers one pipeline stage may complete before the next is started.
>
> I have a general idea of what you're talking about.
> Can you be more precise. How can I bufferize the stages ?

For one, Cocoon does it for you through the caching system. It can be
tuned in various way, still a component that issues data out-of-band
must not implement cachable for example.

Another opportunity to buffer the transformation is when debugging
your pipelines and write the result of a stage to a file....

> >So, you can use request attributes (or session attributes, an external
> >file, ...) to pass parameters out-of-band, provided it is not needed
> >for the following stage any earlier than the tag that causes the
> >parameter to be set.
> 
> I didn't understand that.

naïve, but wrong:

 time     stage n      stage n+1
  0        <foo>
  1        <bar>
  2        </bar>
  3        </foo>------------------------sets parameter
  4                     <foo>------------needs parameter
  5                     <bar>
  6                     </bar>
  7                     </foo>

actual schedule:

 time     stage n      stage n+i

  0        <foo>
  1                     <foo>------------needs parameter, which parameter??
  2        <bar>
  3                     <bar>
  4        </bar>
  5                     </bar>
  6        </foo>------------------------sets parameter
  7                     </foo>

HTH

	Chris.

PS It would be nice if you could reply below the original message. It
makes it so much easier to follow an argument because you can just
read top to bottom.

-- 
C h r i s t i a n       H a u l
haul@informatik.tu-darmstadt.de
    fingerprint: 99B0 1D9D 7919 644A 4837  7D73 FEF9 6856 335A 9E08

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